Riboswitches are RNA-encoded genetic control elements that regulate gene expression in a ligand-dependent fashion. They are comprised of an aptamer domain, which recognizes the ligand, and an expression platform, which couples ligand binding to changes in gene expression. Natural riboswitches are found commonly in prokaryotes, and sometimes in eukaryotes (Lynch et al., Chem Biol 14(2):173-184, 2007). In addition, a number of synthetic riboswitches that respond to non-endogenous small molecules have been developed (Desai et al., J Am Chem Soc 126:13247-13254, 2004; Grate et al., Bioorg Med Chem 9:2565-2570, 2001; Harvey et al., RNA 8:452-463, 2002; Suess et al., Nucl Acids Res 31:1853-1858, 2003; Werstruck et al., Science 282:296-298, 1998). Synthetic riboswitches can be used, for example, to construct synthetic gene circuits, to report on cellular metabolism, or to reprogram cellular behavior (Lynch et al., Methods Mol Biol 540:321-333, 2009).
A microbial consortium is a group of different species of microorganisms that act together as a community. Microbial consortia are ubiquitous in nature and are involved in a number of processes of significant relevance to humans, including wastewater treatment, environmental remediation and assistance in food digestion. There is significant interest in developing synthetic microbial consortia because they can carry out complex tasks that individual organisms cannot and are more tolerant to environmental fluctuations (Brenner et al., Trends Biotechnol 26(9):483-489, 2008).